Is there a simple way to import contacts and have them subscribed automatically to the Opt-In autoresponder, without having to subscribe each of them individually?

When you import a list of contacts, they are NOT automatically subscribed to your autoresponders. So, it does require that they subscribe themselves via your Opt-In forms or that you subscribe them manually, either individually (one by one), or in mass via the Search Contacts tool where you can apply the action of autoresponder subscription to a list of clients. Here is a tutorial about applying mass actions.

IMPORTANT: If you subscribe them yourself, make sure they agreed to receive communications from you. That is also why we cannot implement this functionality of having them subscribed automatically to coach communications during contacts import, as it has potential to be in conflict with SPAM requirements. In any case, the autoresponder messages also include an unsubscribe link in the footer, so the recipient has the option to unsubscribe from your communications.